The present invention relates to a wiring board and production method thereof, and semiconductor apparatus made up thereof.
Increasing speed and density in LSI technology in recent years have come to require a finer size of electronic circuit wires, a multi-layered structure and further improvement of electric characteristics. To meet these requirements, studies have been made to manufacture multi-layered wiring boards made up of organic insulating materials featuring excellent flatness, heat resistance, dimensional stability and dielectric characteristics.
When copper-made wiring is formed on the organic insulating resin substrate, the biggest problem is how to get a close adhesion between the copper wiring and resin substrate. Conventionally, it was the common practice to improve adhesion with the metallic film deposited on the resin substrate surface through anchoring effect or mechanical entanglement by roughening the resin substrate surface by soft-etching it or by placing rubber component into resin substrate in advance and dissolving it with solvent. This method, however, requires tens of microns of an uneven spot to ensure sufficient adhesion. It has been difficult to create fine wiring having a line width not exceeding tens of microns. It has been required to develop a method of accelerating adhesion which ensures a high adhesion merely by creating an uneven spot sufficiently smaller than wiring/space interval on the surface, wherein adhesion does not degenerate even at a high temperature.
Subtract and additive methods are known as methods for forming copper wiring on the organic insulating resin substrate. The subtract method produces wiring circuits by metalizing copper over the entire substrate, thereafter removing by etching the copper of the portion which is unnecessary as wiring. To metalize copper over the entire substrate, CVD and spatter methods are generally used. According to another proposed method, a thin layer of copper is plated onto the entire substrate by thin electroless copper plating, and electric copper plating is used to deposit a thick layer of copper thereafter. For example, the Patent Official Gazette of Japanese Patent Laid-Open NO.187778/1992 discloses a method of depositing copper onto the entire polyimide to a thickness of about 0.3 xcexcm by electroless plating, following by application to a thickness of about 35 xcexcm by electroplating. The subtract method requires the copper plate having a thickness not less than 10 xcexcm to be etched onto the resin substrate, with the result that the side of the copper wiring line must be etched, and the side close to the substrate of the wiring line becomes thin. This makes it difficult to produce a fine line/space pattern. It has been possible to create a line/space pattern of about 40 xcexcm at most.
The additive method, on the other hand, is a method of producing a circuit pattern on the substrate by resist and depositing conductive metals along said pattern. This method is suited for production of fine wiring because the aspect ratio of copper wiring line is equivalent to the resolution of the resist. This additive method can be further divided into semi-additive and full-additive methods.
According to the semi-additive method, a thin layer of metal is deposited on the entire substrate, then plated resist is created. After that, a thick layer of conductive metal or copper in many cases is plated by electro plating or electroless plating. Subsequent to separation of the resist, the ground metallic film is etched out, thereby producing wiring. It is the common practice to apply a very thin layer of copper by electroless plating onto the copper-plated laminate with copper etched out, and to apply a thick layer of copper by electroplating or electroless plating subsequent to resist formation. After separation of resist, the thin copper film is etched out. This method is suited for the substrate with its surface having tens of microns of an uneven spot, such as the copper-plated laminate with copper etched out, but cannot be used for a more smooth substrate since effective adhesion cannot be ensured. To get higher adhesion, a method is proposed wherein metal other than copper is plated on the substrate; then a thick layer of copper is plated thereto. For example, the Official Gazette of Japanese Patent Laid-Open NO.65061/1998 discloses a method wherein a ground metallic layer is formed on the insulating film by vapor deposition or sputtering dry plating method, and electroless plating followed by electroplating is provided thereon. This method is alleged to permit wiring boards to be produced in a semi-additive method. The ground metallic layer is formed on the insulating substrate, and resist is formed thereon. Then a thick layer of copper is plated by electroplating, and the ground metallic layer is etched out after separation of resist, with the result that fine wiring having dimensions as close to those of the resist is formed. When ground metal and copper coexist, however, it is very difficult to etch only the ground metal. Furthermore, when ground metal is etched out, the copper wiring and ground metal portion thereunder have different width. A slight clearance may be produced between the insulating substrate and ground metal layer. This will raise a problem that, when the wiring board is laminated with insulating adhesive resin, this clearance is not sufficiently filled with adhesive resin, and remains as void.
According to the full additive method, the substrate is provided with plating catalyst; then plated resist is provided. Conductive metal, for example, copper electroless plated, and the resist is separated or is left as permanent resist, as required, thereby producing the wiring board. Since there is no process of etching out the thin ground metallic film, the number of processes is reduced. Since the form of wiring is determined by the form of resist, this method is advantageous to the formation of fine wiring, so the full-additive method is more preferred. Furthermore, even when ground metal other than copper is used, there is no etching process. Since the form of the conductor is determined by the form of resist, there is no problem of a clearance being produced between the insulating substrate and ground metallic layer, as observed in the semi-additive method. However, one of the big problems with the full additive method is that it is difficult to provide electroless plating to the resin substrate with excellent adhesion. A method is proposed to roughen the resin substrate in order to realize tight adhesion. In creating a fine line pattern not exceeding 40 xcexcm, it has been difficult to use the substrate having an uneven spot not less than microns. For this reason, it has been required to develop a method for providing electroless copper plating on the resin substrate having an uneven spot which is sufficiently smaller than width of the line/space pattern, said plating ensuring a high adhesion free from separation even during electroless plating. The Official Gazette of Japanese Patent Laid-Open NO. 72070/1992 discloses that a high adhesion can be obtained by etching the polyimide resin substrate and providing catalyst, followed by electroless plating and heat treatment at 120xc2x0 C. or more. However, this Official Gazette failed to provide a thick layer of one micron or more by electroless plating.
The object of the present invention is to provide a wiring board having a fine wiring layer featuring high adhesion, production method thereof, and semiconductor apparatus.
The present invention relates to a wiring board characterized in that a wiring layer comprising a plated film having a line width of 10 to 40 xcexcm, preferably 15 to 35 xcexcm, and a thickness of 15 to 45 xcexcm, preferably 15 to 35 xcexcm is formed on an insulating resin substrate through the degenerated layer formed on the surface of said insulating resin substrate, and the average roughness at the centerline of said substrate of at least the portion where said wiring layer is formed is equal to or smaller than 1.0 xcexcm, preferably in the range from 0.05 to 0.3 xcexcm.
The present invention is characterized in that a wiring layer is located on the insulating resin substrate, and said wiring layer is formed through the degenerated layer including the amide group formed on said resin substrate surface, and various layers including a metallic oxide layer.
The present invention relates to a wiring board characterized in that said board has wiring on an insulating resin substrate, and said wiring layer is formed through the degraded layer wherein the average roughness at the centerline of said substrate surface formed on the surface of said resin substrate is 0.1 to 1.0 xcexcm, preferably in the range from 0.3 to 0.7 xcexcm, and various layers including a metallic oxide layer formed on the surface of said wiring.
Said wiring layer is preferred to be formed by sequential lamination of a catalyst layer, electroless plated film and electroplated film on the surface of said metallic oxide layer.
The present invention is intended for formation of fine wiring having a line width equal to or smaller than 40 xcexcm with excellent adhesion, and, for this purpose, ensures that the average roughness at the centerline on the surface of the insulating resin substrate is kept equal to or smaller than 1.0 xcexcm. So far, such surface roughness has failed to ensure a high adhesion; however, formation of such fine wiring is provided by the processing adopted in the present invention. Furthermore, the size equal to or smaller than 40 xcexcm can be obtained in the line/space pattern. This size is preferred to be 10 xcexcm, and is more preferred to be in the range from 20 to 35 xcexcm. Such fine wiring can be obtained by using a peeling strength of 300 N/m or more. In particular, the value obtained by a peeling strength (N/m) multiplied by line width (xcexcm) should be equal to or greater than 10,000, preferably equal to or greater than 15,000, and more preferably equal to or greater than 20,000. Peeling strength is preferred to be higher as the line width is smaller. For the wiring layer, the value obtained by multiplying the line width by thickness thereof is preferred to be in the range from 400 to 1200 xcexcm2, and is more preferred to be in the range from 500 to 800 xcexcm2.
The present invention generates amide group by modifying the surface of the resin substrate featuring excellent heat resistance and dimensional stability, and the metal having a reduction potential more base than that of copper is deposited thereon. The oxide layer of said metal is formed at the interface of the two, then copper is deposited on said metal to raise adhesion between the resin substrate and copper and to minimize degeneration of adhesion at a high temperature, thereby getting an extremely reliable wiring board. Copper wiring is formed on the resin substrate according to the full-additive method which is very effective for the formation of fine steel wire having a line width of tens of microns on said resin substrate.
The inventors of the present invention have studied to find out the chemical interaction which improves adhesion between the resin substrate and metal to be deposited, and has succeeded in locating a very powerful interaction is applied between the amide group and metallic oxide film.
The present invention is preferred to be composed of (1) an insulating resin substrate, (2) a metallic film deposited on said insulating resin substrate, (3) a layer including the amide group formed on the surface on the side of said resin substrate at the interface between said metal and said resin substrate, and (4) metallic oxide film formed on the surface on said metallic film side at said interface; and wiring with said metallic film as a conductor is preferably provided on said resin substrate.
The wiring board where wiring with copper as a conductor is provided on the insulating resin substrate according to the present invention is preferred to be formed by sequential lamination of (1) a degenerated layer formed on said insulating resin substrate by plasma treatment of said insulating resin substrate, (2) a metallic oxide layer of the metal having a reduction potential more base than that of copper, (3) a metallic layer of said metal, and (4) a copper layer.
The metal having a reduction potential more base than that of copper according to the present invention is preferred to contain at least one of nickel, tin and cobalt.
In the production of a wiring board wherein wiring with copper as a conductor provided on the insulating resin substrate according to the present invention, the present invention comprises (1) a step of providing plasma treatment on the surface of the resin substrate comprising the resin where the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C., (2) a step of providing the metallic layer of the metal having a reduction potential more base than that of copper on the plasma-treated surface of said resin substrate by electroless plating, (3) a step of forming an oxide layer of said metal at the interface between said metallic layer and said resin substrate in contact therewith, and (4) a step of forming a copper layer on said metallic layer by electroless plating.
In the present invention, plasma treatment is preferred to be provided on the insulating resin substrate in such a way that average roughness at the centerline on the treated surface will be within the range from 0.1 (inclusive) to 1.0 xcexcm (inclusive).
In the present invention, a step of providing plating catalyst on the plasma-treated surface of said resin substrate and a step of forming a plated resist are preferred to be provided between the step of providing plasma treatment on the resin substrate and the step of providing a metallic layer on the plasma-treated surface of said resin substrate.
The wiring board according to the present invention comprises multiple wiring resin layers provided with wiring made up of a metallic conductor on an insulating resin substrate, and has an opening on the surface and a bonding pad to permit electric connection with ICs inside said opening;
wherein said wiring board is characterized in having a conductor comprising a lamination of
(1) a resin layer comprising the resin where the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C.,
(2) a first metallic layer containing at least one of nickel, tin and cobalt, and
(3) a second metallic layer different from the metal contained in said first metallic layer.
Furthermore, the present invention provides a wiring board comprising the lamination of a ceramic wiring board using ceramic as an insulating layer and a resin wiring board using resin as an insulating layer to ensure electric connection between the two;
wherein said wiring board is characterized in having a conductor comprising a lamination of
(1) a resin layer comprising the resin where the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C.,
(2) a first metallic layer containing at least one of nickel, tin and cobalt, and
(3) a second metallic layer different from the metal contained in said first metallic layer.
The present invention provides a method for producing a wiring board where wiring with copper as a conductor is provided on the resin substrate; wherein said method comprises;
(1) a step of using aqueous solution containing alkaline metallic hydroxide to form a layer containing amide group by hydrophilic treatment of the surface of the resin substrate made up of the resin where the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C.,
(2) a step of causing the metal film having a reduction potential more base than that of copper to be deposited on the layer containing said amide group,
(3) a step of causing a metallic oxide film to be deposited on the surface of said metallic film at the interface between said metallic film and said layer containing amide group, and
(4) a step of electroless plating on said metallic film, thereby causing copper to be deposited.
FIG. 1 is a cross sectional view of a wiring board. When one type of metal is used on the resin substrate, an amide group-contained layer 12 or a degenerated layer formed by plasma treatment are located on the resin substrate side at the interface between resin substrate 11 and metallic layer 14, while metallic oxide layer 13 is found on the metallic layer side. When more than one type of metal is used on the resin substrate, a second metallic layer is formed on said metallic layer. Especially when the second metal is copper and copper is formed by electroless plating, the first metal has a reduction potential more base than that of copper.
A highly heat-resistant insulating resin substrate related to the present invention includes polyamide resin, polyimide resin, polybenzoxazole, polyamide-imide resin, polybenzimidazole resin, aramid resin, and epoxy resin. Especially when a thick layer of copper is formed by electroless plating, it is preferred to meet the requirement that the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C.
A highly heat-resistant resin substrate with amide group contained in the skeleton includes polyamide resin and polyamide-imide resin. A highly heat-resistant resin substrate permitting introduction of amide group on the surface by chemical surface treatment includes polyimide resin prepared by dehydration and condensation of acid anhydride and amine, and polybenzoxazole prepared by heating and dehydration of polyamide. For the resin without functional group serving as an amide group, for example, polyethylene and epoxy resin, amide group can be generated by introduction of carboxyl group on the surface by strong acid treatment and by reaction of it with amine. Evaluation of adhesion with metal plated thereon subsequent to surface modification for generation of amide group or plasma treatment has revealed that polyimide resin exhibits an especially high adhesion. This shows that polyimide resin is particularly preferred as a resin substrate.
In the case of plasma treatment, surface shape generally depends on the type of reaction gas to be used. Independently of whether reaction gas to be used is oxygen or nitrogen, adhesion is higher when the average roughness at the centerline on the surface of the degenerated layer is 0.1 xcexcm or more. It has been possible to get close adhesion capable of withstanding the practical process where the peeling strength in the pull-put peel test at 90 deg. is 500 N/m or more at a temperature of 25xc2x0 C. This suggests that oxygen and nitrogen are preferred as reaction gas. From the view point of adhesion, plasma treatment is preferred to be carried out to ensure that average roughness at the centerline on the treated surface on the surface of the degenerated layer including the amide group to be formed will be 0.1 xcexcm or more. On the other hand, if the resin substrate surface is roughened to the extent to which the average roughness at the centerline reaches 1.0 xcexcm or more, uneven spots of wiring cannot be ignored when creating a fine wiring with a line/space interval of 10 to 40 xcexcm, preferably 15 to 30 xcexcm, in particular, about 20 xcexcm. The degenerated layer itself is embrittled. To avoid such problems, the average roughness at the centerline is preferred to be 0.1 xcexcm or more, and 1.0 xcexcm (inclusive) to 0.15 through 0.35 xcexcm.
Nickel, cobalt, titanium and chromium can be cited as examples of the metal having a reduction potential more base than that of copper. The metallic layer and copper can be deposited by sputtering, but use of electroless plating is preferred to create a wiring pattern using the full additive method suited for formation of fine wiring. Said metallic oxide layer can be formed by causing a thin layer of said metal to be deposited on the resin substrate in advance and by subsequent oxidation thereof. Or it can be formed by allowing said metal to be deposited on only one side of the resin substrate and putting it in oxygen atmosphere to supply oxygen to the interface through the resin substrate. Interaction between the surface of the resin substrate subjected to amide group generation and metallic oxide layer requires that they are placed in contact with each other. It does not require particular thickness thereof.
Copper on the top layer can be formed by sputtering or electroplating. However, use of electroless plating is preferred when a wiring board is produced according to full additive method.
A wiring pattern can be produced by (1) so-called subtract method where the wiring pattern is created by etching with a proper resist after metal is deposited on the entire resin substrate, (2) a semi-additive method where resist is applied after a thin layer of of metallic film having been plated on the entire resin substrate, and a thick layer of metal is plated by electroplating or electroless plating, followed by a step of etching out the unwanted portion of the thin layer of metallic film, or (3) a full additive method where conductive wiring is created by plating a thick layer of metal by electroplating or electroless plating after resist has been applied.
To generate a wiring board according to the full additive method, the following process can also be considered: After plating catalyst has been applied to the entire plasma-treated resin substrate, light sensitive dry film is laminated on the resin substrate surface, or light sensitive insulating resin coating solution is coated and dried, and plated resist is formed by exposure and development. Post-exposure and development will be performed if required. Then a metallic layer of the metal having a reduction potential more base than that of copper is formed by electroless plating. An oxide layer is formed at the interface between said metallic layer and said resin substrate by heat treatment carried out after formation of this metallic layer. After removal of the oxide film from the surface of said metallic layer with dilute hydrochloric acid, it is put into an electroless copper plating bath to plate a required volume of copper, thereby completing production of a copper wiring board.
A wiring layer can be laminated by repetition of a step of coating the insulating resin coating solution on the conductive wire and drying it and a step of forming the conductive wiring. The insulating layer is made flat by grinding, as required. When an insulating resin film is used as an insulating layer, conductive wiring is formed on the resin film and conductive wiring sheet is created. Another conductive wiring sheet is laminated thereon with an adequate adhesive sheet held in-between, and heat and pressure is applied, thereby completing lamination. Electric connection between layers can be easily achieved by formation of a via-hole with laser beam and by plating inside the via-hole or filling of conductive paste.
Depending on the purpose of use, the wiring board according to the present invention can be used as a flexible wiring board independently by itself, or can be used as a rigid wiring board when it is mounted on the ceramic or glass plate or silicon wafer. Furthermore, it can be used as an integral wiring board when the wiring board according to the present invention is mounted on the ceramic wiring board, and electric connection between the two is provided. Still further, wiring board according to the present invention allows easy mounting of multiple ICs on the surface; therefore, it can be used as a multi-chip module board. Especially, this is suited as a multi-chip module board where multiple ICs are mounted, since formation of fine copper wiring is ensured by full additive method.
The inventors of the present invention have found out that adhesion is improved by specific functional group and metallic oxide.
When polyimide is treated by alkaline aqueous solution, imide ring is opened close to the surface, and amide group is formed. This has been confirmed by measurement of total reflection infrared absorption spectrum. FIG. 2 shows the total reflection infrared absorption spectrum before and after treatment when Kapton 200H by Dupont is used as polyimide. FIG. 3 shows the difference spectrum. New absorption belts appear in the vicinity of 1650 and 1550 cmxe2x88x921 by surface treatment. They are attributable to amide I and amide II absorption belts, respectively. It can be seen from the changes in the spectrum that the imide ring is open and an amide group is formed. Plating catalyst (HS-101B by Hitachi Kasei) is added on this surface, and electroless copper plating solution (CUST-2000 by Hitachi Kasei) is used to carry out copper plating. The temperature of plating solution was 40xc2x0 C. and plating time was 3 sec. After sufficient drying by vacuum drying subsequent to plating, the test piece was discharged into the air for 24 hours. FIG. 4 shows the changes in said difference spectrum before and after plating. A clear change was observed on amide I and amide II absorption belts before and after plating. This change clearly shows presence of interaction between amide group and copper plated film.
About 30 nm of copper film was deposited on the surface-treated polyimide by said electroless copper plating. A thick layer of about 20 xcexcm of copper was deposited by copper electroplating. Adhesion was evaluated in a peel test. Immediately after copper electroplating, there was almost no peeling strength. When it was left to stand in air, there was a considerable improvement of adhesion with time. Especially when left in the oxygen atmosphere after vacuum drying immediately after copper electroplating, a conspicuous increase in the peeling strength was observed. FIG. 5 shows the secular change of the peeling strength. This result clearly shows that, if copper oxide film is formed at the interface between polyimide and plated steel film, there is a considerable improvement in adhesion of the both. Therefore, a very strong interaction is applied between the amide group and copper oxide, and adhesion is applied. The same result was observed in other types of polyimide and metal except for copper, for example, in the combination of nickel, cobalt and titanium. Furthermore, this result is not restricted to polyimide resin. It was observed in other resins, for example, in polybenzoxazole, polyimide resin and benzimidazole. Namely, it has been found out that the same result can be obtained from introduction of the amide group on the surface of the resin by hydrolyzation.
Authors of the present invention have found out in the peel test that, similarly to the layer containing said amide group, a very strong interaction is applied between the degenerated layer formed by plasma treatment and metallic oxide film; therefore, a very powerful adhesion is ensured.
The authors of the present invention has found out a drastic improvement of adhesion between the resin material and said metallic layer resulting from formation of oxide layer of said metal at the interface, subsequent to formation of the metallic layer of the metal having a reduction potential more base than that of copper by introduction of amide group into the surface of resin material or plasma treatment. They have also found out that a thick layer of copper can be formed on this metallic layer by electroless plating, subsequent to creation of interface of such high adhesion.
Resin material featuring excellent heat resistance, dimensional stability and dielectric characteristics is suitable as a substrate material when using polyimide resin in the wiring board. An important point is that it has an excellent alkali resistance. In the electroless copper plating bath, reaction must take place wherein that reducing agent such as formaldehyde is oxidized on the surface of metallic copper. Alkalinity is essential for this reaction to take place. This means that wiring substrate material is exposed to alkaline solution for a long time. If alkali resistance is low, the substrate as a basis is melted during electroless copper plating, and plated copper film is separated. This has been observed in the study by the authors of the present invention. So they studies the relationship between alkali resistance and electroless copper plating resistance. Etching velocity in the mixture solution of hydrazine and ethylenediamine (70 to 30% by weight) kept at a solution temperature of 30xc2x0 C. was used as an index to show alkali resistance. Polyimide resin was used since it provides high polymers having various structures by a combination of diamine and acid anhydride. As a result of this study, it has been confirmed that that the plated film deposited on the substrate does not separate even when plating is carried out for 15 hours or more in electroless copper plating bath of about pH 12 kept at a temperature of 70xc2x0 C., if the etching velocity does not exceed 1 xcexcm/min. It has been made clear that this condition is not restricted to polyimide resin alone; it is applicable to other resins such as polybenzoxazole, polyamide resin, polyamide-imide resin, polybenzimidazole resin, aramid resin, and epoxy resin.
Then study was made to find out how to get a sufficient adhesion between copper and resin substrate when said resin substrate surface is subjected to electroless copper plating. The substrate surface was modified under various conditions; then vapor deposition of copper was provided about 1 xcexcm by sputtering. Then a thick layer of copper was provided by electroplating until a film thickness of 20 xcexcm was reached, and the peeling strength was evaluated. This study has shown that effective methods are provided by treatment of the resin substrate surface with alkaline solution, and by surface treatment through plasma treatment using oxygen and nitrogen as reaction gas. Especially when plasma treatment is used, a very high adhesion was ensured by formation of an uneven spot of 0.1 xcexcm or more with the average roughness (Ra) at the centerline on the resin substrate surface. For example, peeling strength in 90-deg. pull-out peel test at 25xc2x0 C. is 500 N/m or more. It has become possible to get close adhesion capable of withstanding actual wiring board production process.
Plating catalyst was added to the resin substrate provided with said surface modification, and the substrate was plated in an electroless copper plating bath. Despite the pH value of 10 to 13 and plating bath temperature of 20 to 80xc2x0 C., the plated film was separated when copper film was about 30 nm or less. When electroless copper plating of a thick layer was conducted after flash electroless copper plating of a thin layer, the plated film was separated immediately after electroless copper plating of a thick layer, with the result that a thick layer of plating failed. Thus, it has been found out that adhesion between the modified resin substrate surface and copper is considerably reduced in electroless copper plating bath. So various studies have been made to examine electroless copper plating after application of metallic film other than copper on the resin substrate surface. It has been revealed that separation of plated film does not take place during plating by performing electroless copper plating after application of metallic film of nickel, tin and cobalt. Study of various types of metals has shown that it is effective to apply the metal having a reduction potential more base than that of copper in advance. At the same time, it has been shown that adhesion between the resin substrate and metallic film is considerably improved through formation of metallic oxide film between the resin substrate and metallic film by placing resin substrate in the oxidation atmosphere after deposition of metallic film on said resin substrate. For example, the surface of polyimide resin substrate was treated with alkaline solution, and a film thickness of about 1 xcexcm of nickel was deposited on that surface by electroless plating. Then a thick layer of copper was deposited on the nickel to a film thickness of about 20 xcexcm by electroless copper plating, thereby evaluating the adhesion between polyimide and nickel. Comparison of the peeling strength between the sample provided with annealing in the atmosphere at 180xc2x0 C. for two hours after nickel plating and untreated sample shows 900 N/m and 300 N/m, respectively. Improvement of adhesion by annealing after plating was also observed when plasma treatment was conducted as resin surface treatment. This is considered to be due to chemical interaction with the surface of the resin where oxide at adhesive interface contains amide group or the surface of the plasma treated resin.
As a result of the above studies, the authors of the present invention have completed the present invention by finding out that a thick layer of copper film can be formed on said metallic layer by electroless copper plating by taking the following steps: (1) the resin where the velocity of dissolving the mixture solution of hydrazine and ethylenediamine mixed at the ratio of 7 to 3 does not exceed 1 xcexcm/min. at a solution temperature of 30xc2x0 C., was used as a resin substrate; (2) amide group was introduced into the surface of resin material or plasma treatment was conducted; (3) the metal having a reduction potential more base than that of copper was deposited on the treated surface; and (4) oxide layer of said metal was formed at the interface between said resin substrate and said metal layer.
Furthermore, the authors of the present invention have found out that fine copper wiring having a line/space pattern of about 20 xcexcm with a film thickness of of about 20 xcexcm and with a high aspect ratio can be formed on the resin substrate by the following steps: (1) Catalyst is applied to the resin substrate where amide group is introduced or plasma treatment is made; (2) then dry film is laminated thereon; (3) then plated resist is formed by exposure and development. For example, after nickel is deposited by electroless plating, nickel oxide film is formed at the interface between resin substrate and nickel by baking in the atmosphere. After nickel oxide film is removed from the surface it is put into the electroless copper plating bath to provide a thick layer of copper.
The present invention provides highly reliable wiring boards characterized by excellent adhesion between conductive metal and resin substrate, and superb heat resistance. This provides fine wiring having a required thickness with a line width of 40 xcexcm or less.
A highly reliable multi-chip module featuring excellent heat resistance is provided by forming a laminated board through lamination of said multiple wiring boards wherein electric connection is made between layers, and a connection port with ICs is provided on the outermost surface to mount the ICs.